This invention relates to an electrical connection structure for a stationary terminal and a movable piece in a micro switch or the like.
One example of a conventional micro switch is as shown in FIGS. 22 and 23.
The micro switch comprises: a stationary terminal 1 which is a common terminal, and a pair of stationary terminals 4 and 5 which are fixedly inserted in a resin casing 9; a switching movable piece 3 having its base end portion engaged with a V-shaped engaging groove formed in one engaging piece 1a of the stationary terminal 1 (hereinafter referred to as "an armature 3", when applicable), and a movable contact 3a provided on its free end portion in such a manner that the movable contact appears on both sides (the upper and lower surfaces) of the free end portion; a movable spring 7 for operating the armature with a snap, the spring 7 having its base end portion engaged with a V-shaped engaging groove 6 formed in the other engaging piece 1b of the stationary terminal 1 and its free end portion engaged with the free end portion of the armature 3; and a push button 8 supported by the casing in such a manner that it is pushed against the middle of the armature 3 when depressed. In the normal state of the micro switch; that is, when the push button 8 is not depressed yet, as shown in FIGS. 22 and 23 the free end portion of the armature 3 is urged upwardly by the elastic restoring force of the movable spring 7, so that the movable contact 3a is held in contact with the contact of the stationary terminal 4 (which is a normally closed contact). When, under this condition, the push button 8 is depressed, the middle of the armature 3 is displaced below a predetermined position, instantaneously the armature 3 is urged downwardly by the elastic restoring force of the movable spring 8 (snap action), so that the movable contact 3a is tripped over to the contact 5a of the other stationary terminal 5 (which is a normally open contact). Thus, the switching operation has been accomplished.
In the above-described micro switch, the contact resistance of the switch occurs not only in a portion between the contact 3a and either of the contacts 4a and 5a but also in each of engaging portions between the stationary terminal 1 and the armature 3, between the movable Spring 7 and the stationary terminal 1 and between the movable spring 7 and the armature 3.
However, the frequent slide motion in the engaging portions makes the contact resistance unstable, as a result of which the switch is liable to become low in contact reliability. Furthermore, sometimes the micro switch suffers from the following difficulty: When the contact resistance increases, heat is generated to increase the temperature of the micro switch, thus adversely affecting the durability of the latter. Thus, there is much room for improvement in the durability of the conventional micro switch.
In order to improve the contact between the engaging groove 2 and the armature 3 in reliability, there has been proposed a method in which the engaging portions of the engaging groove 2 and the armature 3 are plated with silver. However, the method is not economical because the sliver plating will increase the manufacturing cost of the micro switch.
In order to improve the reliability in electrical connection of the stationary terminal 1 and the armature 3, a method has been proposed in which, as shown in FIG. 21, both ends of a lead wire 12 are soldered to the portions of the stationary terminal 1 and the armature 3 which are less displaced from each other. However, the method is also disadvantageous in that the number of components and the number of manufacturing steps are increased as much, and accordingly the manufacturing cost is increased.